Native endophytes from maize as potential biocontrol agents against bacterial top rot caused by cross-kingdom pathogen Klebsiella pneumoniae

Maize crop has been suffering huge economic loss due to bacterial top rot disease caused by emerging plant pathogen Klebsiella pneumoniae, which is most concerning and highly contagious to both humans and animals. At present, chemical control is considered as an important disease management approach, however biological control through native endophytes has not been reported yet. Here, initially we isolated 120 native endophytes from maize plants, and screened 12 endophytes with potential antagonistic effect in coculture assay against maize bacterial top rot pathogen. Based on strong antibacterial activity, three endophytes (MZ-4, YN-23, and F14) were selected to evaluate their plant growth-promoting traits and biocontrol efficiency through in-vitro and in-vivo antagonistic assays. The three strains could produce IAA with a maximum yield of 2.54 mu g/ml, 2.96 mu g/ml, 2.07 mu g/ml, respectively and also inhibit the growth of 10 common plant pathogenic bacteria. In planta assay suggested that three endophytes enhanced maize growth and significantly suppressed the incidence of K. pneumoniae with control effect of about 81.2 %, 74.7 %, and 66.7 %, respectively. Lastly, selected isolates MZ-4, YN-23, and F14 were molecularly characterized and identified as Bacillus velezensis. To our knowledge, this is the first study reporting the application of maize endophyte B. velezensis as a biocontrol agent against emerging pathogen of maize bacterial top rot disease.